The changes in glycogen concentrations during and following ischemic episodes were studied. Mongolian gerbils were made ischemic by occlusion of the left carotid artery. After either 1 or 3 hours of occlusion, glycogen levels in the ischemic cortex were 10% of control. Following recirculation, glycogen levels were normal after 1 hour in both ischemic groups. After 1 week of recirculation, glycogen levels were twice normal concentrations in animals that had been ischemic l hour. In the 3 hour ischemic group, glycogen concentrations increased to 170% of control after 5 hours of recirculation. In this group, glycogen was still elevated after 20 hours or 1 week of recirculation.